Refrigeration systems often use various types of heat exchangers, such as plate-to-plate, co-axial or shell and tube, as an evaporator or a condenser. In many applications, shell and tube heat exchangers are employed as condensers. However, shell and tube type heat exchangers suffer from several drawbacks and limitations.
In certain condenser applications, heat exchanger tubing can become clogged if the supply fluid is not cleaned. Unlike plate-to-plate and co-axial heat exchangers, shell and tube heat exchangers can be cleaned, but this is often difficult, time consuming and messy. Generally, the cleaning of a shell and tube exchanger requires removal of the shell-and-tube heads and the gasket positioned between the heads and the shell body. This takes time and often requires special tools. Further, when the cleaning operation is complete, a replacement gasket must be repositioned and the heads reattached. This operation again can be time consuming and improper positioning of the new gasket, improper coupling of the head to the shell, or failure to use a new gasket can render the exchanger inoperable.
In addition, shell and tube heat exchangers are often limited in terms of the flow patterns they can provide for the shell-side fluid relative to the tube-side fluid. Conventional shell and tube heat exchangers generally provide for “cross-flow” between the fluids. The availability of only cross-flow in conventional shell and tube heat exchangers is often limiting on the performance that can be obtained from such devices. Conventional shell and tube exchangers are often restricted to specific flow circuit arrangements or are costly to modify.
A still further limitation of conventional shell and tube exchangers is their size. Because conventional shell and tube exchangers typically include a large number of tubes positioned within an even larger shell, the overall size of such exchangers is often quite large and, typically, well over six inches in outer diameter. Moreover, because of the design of shell-and-tube exchangers, the design of the unit is often restricted to a particular configuration and shape and is further restricted to a unit that must be positioned in a horizontal orientation. The large size and configuration requirements of such shell-and-tube exchangers not only causes problems in terms of space and positioning requirements but it also often requires that the shell, in essence a large pressure vessel, include a pressure relief valve and meet various other standards, for example pressure vessel codes promulgated by the American Society of Mechanical Engineers (ASME), that apply to large pressure vessels.
The size drawback resultant from shell-and-tube exchangers is becoming even more problematic as regulations controlling the use of various refrigerants are implemented. Many conventional shell-and-tube exchangers were constructed to utilize azeotropic refrigerants. Regulations are being implemented that will require the use of non-azeotropic refrigerants such as R-407C. In general, non-azeotropic refrigerants are less effective than azeotropic refrigerants. As a result, to achieve the same general performance, a shell-and-tube exchanger designed to operate with non-azeotropic refrigerants must be sized approximately 20% larger than a similar shell-and-tube exchanger designed for azeotropic refrigerants. Such a size increase further exacerbates the size difficulties posed by shell-and-tube exchangers.
The size limitations posed by shell-and-tube exchangers is still further exacerbated when such exchangers are used as condensers or when sub-cooling or de-superheating is required. In certain cases, when a shell-and-tube exchanger is used as a condenser, an external receiver tank may be used for storing the refrigerant necessary to operate the system. The external receiver tank requires yet more space. Similarly, if sub-cooling or de-superheating is required, a shell-and-tube exchanger must be further oversized or a separate, space-taking, sub-cooler or de-superheater must be coupled to the unit.
The limitations and disadvantages of shell-and-tube exchangers are especially acute in certain applications, such as applications associated with cooling systems for electronic equipment. In such applications, an environmental control unit is typically positioned within a small contained space in a building where the computer servers and other electronic equipment required for the operation of the building are centrally located. Because such rooms are typically perceived as overhead to the main business of an organization, there is a great desire to make the rooms as small as possible. Moreover, because such rooms are typically established in existing buildings, there are often space and sizing requirements. The use of large, size- and configuration-restricted shell-and-tube exchangers in such applications has been of particular concern.
It is an object of the present disclosure to provide solutions to overcome or reduce the above-described and other disadvantages and limitations.